I like changing my oil every 3&3. One reason is to go ahead and lube everything and check my axle lube levels and stuff while I have it on the lift. It much easier for me to do that all at once.
Even with extended drain oils, you should change the filter at least every 5k shouldn't you? Keep the filtration to the max?

Anyhow, I've (well, the Blazer) never liked Purolator and Fram filters. I saw a definite 10-15lbs drop in the oil pressure on the gauge. I used a K&N filter for a while and I didn't see a drop. It was really nice because it had a 1/2" hex head on the end that made it easy to get off. I didn't have to puncture it with a screwdriver to get it turninglike I have to do with the Delco filters. Don't know why, but they seen to get tighter. I hand tighten them as good as I can, then give them another quarter-turn with the wrench.